The term "polyphenylene ether resin" is well known as defining a class of thermoplastic materials which possess outstanding physical properties, including hydrolytic stability, dimensional stability and excellent dielectric characteristics. Methods of preparation are known in the art and described in the patent literature, e.g., Hay, U.S. Pat. Nos. 3,306,874 and 3,306,875 and Stamatoff, U.S. Pat. Nos. 3,257,357 and 3,257,358. Other patents which show the preparation of polyphenylene ether resins include Bennett and Cooper, U.S. Pat. Nos. 3,369,656 and 3,838,102, as well as Cooper and Bennett, U.S. Pat. Nos. 3,642,699, and 3,733,299.
A shortcoming of such thermoplastic materials is that they are thermally unstable at elevated temperatures considerably above room temperature, and even at lower temperatures upon prolonged exposure. As a result, the polymer can undergo oxidation and degradation when extruded or molded, as indicated by a tell-tale yellowish tinge. This imparts an unsightly appearance to the extruded or molded article and can adversely affect mechanical properties as well.
It is known that the thermal oxidative stability of polyphenylene ether resins can be improved by including certain stabilizers with the resin. One such stabilizer is diphenyl decyl phosphite. See also U.S. Pat. No. 2,952,701.
A continuing need exists for ways of improving the thermal oxidative stability of polyphenylene ether resins and compositions containing such resins.